As a recent technical trend, producing a thinner and shorter surface coated member for a cutting tool or the like is on the main stream for the purpose of reducing a load on a global environment and efficiently utilizing a resource. Accordingly, providing a metal material having a higher strength and higher hardness used for a surface coated member is proceeding to secure a service life of a surface coated member and maintain its reliability. On the other hand, at metal working sites, it has been strongly requested to achieve improved accuracy of a worked part and reduced working cost to compete with newly emerging countries. Further, with the improvement in the performance of machining tools, the expectation for further high-speed working with a surface coated member is increasing. In the high-speed working, since a cutting edge of a surface coated member is exposed to a high-temperature and high-pressure environment, a surface coated member capable of having a longer service life even under a harsh environment will be requested in the future.
For example, Japanese Patent Laying-Open No. 7˜205362 (PTD 1) discloses a hard coating which coats a surface of a base member of a surface coated member. In the hard coating, the composition thereof is changed continuously with nitride, carbide, carbonitride, or boride of two or more kinds of elements selected from group 4, 5, 6 elements, Al, and Si at a cycle of 0.4 nm to 50 nm. The above-described hard coating is formed by a PVD (Physical Vapor Deposition) method. Specifically, TiN layers and AlN layers are formed continuously on a base material surface with use of solid Ti, solid Al, and N2 gas by bringing Ti ion and Al ion, which are generated by a vacuum discharge, and N2 gas to be in contact with a base member heated to 500° C. Since the hard coating formed by this method has a large distortion in its structure, a surface coated member having this hard coating can have a superior wear resistance and toughness.
Moreover, for example, Japanese National Patent Publication No. 2008-545063 (PTD 2) discloses a member having a Ti1−xAlxN coating as a surface coated member. This Ti1−xAlxN coating has a single layer structure of a cubic crystal NaCl structure having a stoichiometric coefficient of 0.75<x≦0.93 and having a lattice constant afcc of 0.412 nm to 0.405 nm. The above-described Ti1−xAlxN coating is formed by a CVD (Chemical Vapor Deposition) method. Specifically, a first gas mixture constituted of AlCl3, TiCl4, H2, and argon and a second gas mixture constituted of NH3 and N2 as a nitrogen source are introduced into a CVD reactor vessel of a hot wall type accommodating a base member to perform a thermal CVD method. The above-described coating formed by this method has a higher Al content in the coating as compared to the Ti1−xAlxN coating produced by a generally known PVD method. Therefore, a surface coated member having this coating has a higher oxidation resistance and a higher hardness and can exhibit a superior wear resistance at a high temperature.